Coordination Chemistry I: Structures And Isomers

Coordination Chemistry I:Structures and IsomersChapter 9Friday, November 13, 2015

Coordination ChemistryCoordination compounds compounds that include one or more metal atoms or ions and oneor more ligands that formally donate electrons to the metalLewisAcid LewisBasecoordinate covalent bond – sometimes used to emphasize that aneutral ligand is acting as a Lewis base towards the metal a neutral ligand is one that has no charge when the donor atom has a full octetokay okayan anionic ligand is one that has a formal negative charge when the donoratom has a full octetokaywrong

Coordination ChemistryCoordination compounds neutral coordination compounds include the metal and its boundligands the number of bonds in a coordination complex does not correlatewith the formal oxidation state of the metal coordination complexes can also be charged – complex cations orcomplex anions in a complex ion, the ligands coordinated to the metal make up the primarycoordination sphere there will also be counterions and other ions (and possibly neutral molecules)that make up the secondary coordination sphere

Coordination ComplexesSpecies consisting of a central metal atom/ion bound to a number ofmolecules or ions (called ligands) by coordinate covalent bonds.central metal M: Ni0ligands L: CO (carbonyl)Each ligand has at least one lonepair of electrons with which tocoordinate to the metal. Metal acts as Lewis acid.Ligands act as Lewis bases.tetracarbonylnickel: Ni(CO)4The ligands directly attached to the metalare its first coordination sphere. pale yellow liquid (m.p. -17 C, b.p. 43 C) tetrahedral compound synthesized in 1890 by Mond extremely poisonousThe coordination number of the metalis the number of coordinate bonds to themetal (CN 4 in this case).

Coordination CompoundsThe metal complexhexamminecobalt(III) chloride: [Co(NH3)6]Cl3 solid yellow salt octahedral complex (CN 6) fairly inertThe electricallyneutral compound(complex pluscounter ions) is thecoordinationcompound.Counter ions are notligands. They arepart of the secondcoordinationsphere.

Common Ligands

Polydentate Ligands“Many toothed” ligands. Ligands with lone pairs on more than one atom,capable of binding to a metal at multiple sites. The number of sites by which a ligand binds is called its denticity. Ligands that bind via more than one atom are called chelating ligands.They make chelate (“claw”) complexes.bidentate: entridentate: dientetradentate:porphyrinhexadentate: EDTA

Polydentate LigandsThe denticity of a ligand is its number of donors atoms that coordinateto the metal: monodentate – one donor atom, e.g.,py bidentate – two donors, e.g.,en bpytridentate – three donors, e.g.,dien terpytetradentate – four donors, e.g.,trientren

Polydentate Ligands

Ambidentate LigandsAmbidentate ligands can bind to a metal using either of several atoms.isothiocyanatebinds through Nthiocyanatebinds through Snitro NO2binds through Nnitrito ONObinds through Oyellowred

Formulae & NomenclatureThe complexity of coordination complexes demands strict adherenceto a formal and detailed naming system. consider a coordination compound with the empirical formula PtCl2(NH3)2,which could mean any of the following known H3)3Cl][Pt(NH3)Cl3][Pt(NH3)4][PtCl4]

Formulae & NomenclatureFormulae When writing the formulae of coordination complexes the metal comes firstfollowed by the ligands in alphabetical order (by the ligand name). If the complex is simple, brackets are not needed, for examplemetal oxidation state Ti(NMe2)4 TiIV(NMe2)4 If the complex needs a prefix or is ionic, it is enclosed in square brackets cis-[Pt(NH3)2Cl2] [Pt(NH3)4]2 When both the cation and anion are given, the cation always comes first in theformula K2[PtCl4] K2[PtIICl4] [Pt(NH3)3Cl][Pt(NH3)Cl3] [PtII(NH3)3Cl][PtII(NH3)Cl3]

Formulae & NomenclatureNames1. When writing the names of coordination complexes, the cation always comesbefore the anion2. The ligands are listed alphabetically (by name, not abbreviation or prefix) andcome before the metal3. The number of simple ligands is given by the ‘simple prefix’ below, for complexligands the ‘complex’ prefix is usedNumberSimple PrefixComplex decadecakis

Formulae & NomenclatureNames4. Anionic ligands get an -o suffix (e.g., chloro for Cl–). Neutral ligands keep theirnormal name except for H2O (aqua) and NH3 (ammine)5. There are two ways to deal with charge when naming complexesa. Stock system – the formal oxidation state of the metal is given by Roman numerals inparenthesis after the metal name – more commonly used but sometimes problematicb. Ewing-Bassett system – the charge of the complex is given by regular numbers inparenthesis after the metal name – less common but always correct6. Metals in complex cations keep their normal name. Metals in complex anionsget an -ate suffix, except for the following metals which use their Latin names:MetalAnionic e

Formulae & NomenclatureNames7. Prefixes are used to designate the geometric arrangement of ligands whenneeded.cistransfacmer8. Ligands that bridge two or more metals get a prefix μn-, where n is the numberof metals bridged9. Many ligands have commonly-used names that differ from the IUPAC name,leading to more confusion:LigandCommon NameIUPAC yanato-S–NCS–isothiocyanothiocyanato-N

Formulae & NomenclatureExamplesIn cases where the overall charge on thecomplex is zero, this number is usually notincluded for the Ewing-Bassett system Ti(NMe2)4 tetrakis(dimethylazanido)titanium (0) tetrakis(dimethylazanido)titanium(IV) tetrakis(dimethylamido)titaniumYou’ll see amido muchmore often than azanidoto describe NR2– [Co(NH3)6]3 hexaamminecobalt (3 ) hexaamminecobalt(III)because the entire geometry is defined by asingle cis prefix, a second one is not needed cis-[Pt(NH3)2Cl2] cis-diamminedichloroplatinum cis-diamminedichloroplatinum(II) [Pt(NH3)4][PtCl4] tetraammineplatinum tetrachloroplatinate tetraammineplatinum(II) tetrachloroplatinate(II)

Formulae & NomenclatureExamples trans-[Pt(H2O)2Cl4] trans-diaquatetrachloroplatinum trans-diaquatetrachloroplatinum(IV) [Cu(CH3CN)4][BF4] tetrakis(acetonitrile)copper tetrafluoroborate tetrakis(acetonitrile)copper(I) tetrafluoroborateAccording to IUPAC, it should betriphenylphosphane, but triphenylphosphineis much, much more common cis,fac-[RhClH2(PPh3)3] dium dium(III) dium [(NH3)4Co(μ2-NH2)(μ2-OH)Co(NH3)4]4 μ2-azanido-μ2-hydroxobis(tetraamminecobalt) (4 ) μ2-azanido-μ2-hydroxobis{tetraamminecobalt(III)}

Coordination Chemistry Coordination compounds neutral coordination compounds include the metal and its bound ligands the number of bonds in a coordination complex does not correlate with the formal oxidation state of the metal coordination complexes can also be charged –complex cations or complex anions in a complex ion,